In a method of the aforedescribed kind and an apparatus for carrying out the method, as taught in German laid-open patent specification DE-OS No. 27 41 800 published Mar. 22, 1979, now German Pat. No. DE-P-2741-800, a mold containing ceramic material is hydraulically lifted for being acted upon by a quasi-static pressure, until the piston or the pistons which are mounted on a stationary press yoke have reached a previously adjusted end position in the mold.
In another method for the manufacture of fireproof bricks the ceramic material or sand contained in the mold is subjected to an impact force. The impact force may be obtained by a so called over-pressure hammer, or air hammer, or by means of a friction screw press.
Each of the known methods has specific disadvantages. In the methods using the quasi-static pressure, although the initial costs are relatively low, a limited homogeneity and density is obtained within the bricks when certain sand is used. If an over-pressure hammer, or air hammer is used for carrying out the method using impact pressure, the resultant homogeneity of the bricks, which have been manufactured, is much better, but in view of the high initial costs, and the long processing time, the manufacturing cost of the fireproof bricks is rather high. In view of the functioning of the over-pressure hammer, or the air hammer, the necessary forces are only obtained if the impact piston has a long stroke, or is allowed to fall from a considerable height. Furthermore, in order to achieve the required homogeneity of the manufactured bricks, an impact energy is required, which can only be obtained by lifting the impact piston several times. If friction screw-presses are used, in view of the limited output of the drive, it is not only necessary to increase the processing time, but the pressure force is also limited in view of the inclination between the screw thread and the machine frame, so that the bricks are of a relatively low quality, in spite of the high manufacturing costs.